Friday, February 10, 2012

"Sharks create oxygen" on WhySharksMatter

The sharks and oxygen myth has been getting a lot of attention in the shark conservation community lately. Graduate student David Shiffman who blogs at WhySharksMatter weighs in on his blog today:

Sharks in in no way connected to the global supply of atmospheric oxygen. If every single species of shark went extinct, there would be a variety of negative ecological effects, but a reduction in the global supply of atmospheric oxygen would not be among them. There is not a shred of scientific evidence supporting the idea that the loss of sharks would affect our oxygen supply- not a single scientific paper, not a single technical report. I’ve attended a dozen scientific conferences focusing on marine ecology or shark biology (including three international conferences) and I’ve never seen or heard of anyone presenting or even discussing this. To the best of my knowledge, not a single person who has authored a scientific paper or technical report supports this idea. Despite the complete lack of any kind of credible evidence, and despite many recent blog posts thoroughly debunking it (see herehereherehere here here and here ), this pseudoscience just won’t die.

The premise of the sharks and oxygen claim is as follows:

A) Sharks, many of which are apex predators, are important in regulating marine food webs;

B) Phytoplankton, which create oxygen through photosynthesis, are in marine food webs;

C) Therefore, without sharks, phytoplankton populations will crash and we won’t have any more oxygen and we’ll all die.

A and B are reasonable enough- we know that under certain circumstances, apex predators can play important roles in structuring and regulating food webs, and we know that phytoplankton produce oxygen (though how much oxygen phytoplankton produces is another debate entirely). It’s part C of the sharks and oxygen claim that’s the problem.